The Green Machine

Steves 1988 GPZ900

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Another project that was done in two parts. This seems to be a pattern with me. Do an initial tidy up, ride it for a while, then get stuck into a full restoration.

This GPZ is in similar condition
Part 1

I have a soft spot for Kawasaki GPZ 900's. I owned one of these in the late 80's through early 90's and we did a lot of miles together. I came across this 1988 A5 model a couple of years ago. It was in pretty rough condition so the price was right. You know the story, missing lower fairing, cracks in the upper fairing and side covers, rusted out exhausts and a tired motor. As usual, I do not have any pictures of the bike in its original condition. I was in too much of a hurry to pull it apart. The plan was to get rid of the fairing and the 16 inch anti dive front end as it dated the bike terribly. What I wanted was a naked bike with styling cues from earlier classic Kawasaki's. It needed to look like a factory bike, not a street fighter. A few performance enhancements were also on the cards, the motor needed work anyway.

I started by stripping the bike down and giving it a thorough clean up. The front and rear suspension was removed along with the engine top end. The paintwork on the frame and crankcases was in pretty good nick so I just touched them up. The top end went of to be bored out to 1000 cc and given a port job. The cams and rockers were chewed out (common with GPZ's) so they went to camshaft engineering for hard facing and a mild performance grind. The engine went back together with new seals, cam chain, clutch and a set of Keihin 35mm CR Carbs as the standard ones had worn slides. Air is supplied by the biggest set of K&N's that I could get to fit and the exhaust exits via a stainless Micron 4 into 1.

This thing should really move out when it is sorted. You should see the view when the filters are off and you shine a light through the CR's down the throat of the inlet ports. Speaking of the CR's, these things are so physically big that there is no room for the standard fuel tap. I had to make up an adapter to run a line straight from the tank to a remotely mounted electric fuel tap. I got this from a company that does LPG gas conversions on cars.

The front end and wheels are from a 1991 GPZ900. This upgrade gives me 3 spoke mags with a 17 inch front wheel, larger 41mm forks and 4 pot brake calipers. The only trouble with buying parts from wreckers is that you occasionally get caught. This happened with the front disks. It turned out that they were warped so I had to get a set of EBC disks. Good gear, but I could have done without the extra expense. Brake hoses are braided of course. The front guard is a Yamaha TRX850 fibreglass replica.

Just about ready for paint
I was after the retro look and wanted conventional bars and clocks. It took me ages to find a solution that did not involve too much work. I really wanted Z1 style instruments off a Kawasaki Zephyr 750 or 1100. I had just about given up when I stumbled across a set at the wreckers. They had some accident damage but luckily this was restricted to a few plastic bits that could be replaced easily.

Once the clocks were sorted I went down to the local Kawasaki dealer and measured up a few bikes. I found that the top triple clamp from a ZRX750 has the correct instrument mounts, fork size and offset for the job. All I had to do was make up a sleeve to handle the GPZ's smaller diameter head stem bolt and grind off the mounts for the standard ignition switch. I used an accessory Honda 750/4 switch with a sheet metal adapter welded to the Zephyr instrument bracket. The accessory RD350LC 7 inch headlight is mounted using standard ZRX750 brackets. The wiring turned out to be relatively easy as the most of the colour coding was the same.

After a great deal of polishing, painting, and the odd bit of Nickel plating I had my proof of concept. The bike is far from finished, but I wanted to get it together and run it in to see what else needs sorting. So what's it like to ride? Not as smooth down low as the standard bike, but what can you expect with the big carbs, cam etc. I only have 300 K's on a super tight engine at the moment so I am being pretty careful. Seems to come on with a rush around 5 grand but I wont go any harder until I get a few more miles up. The standard rear shock is definitely cactus. The thing bounces around like a pogo stick.

So what's next? First I have to run it in and get the jetting sorted. Then I have to fit a new rear shock. Once the mechanical details are finished with, it will be time for a paint job. Right now I am thinking of a two tone green like the old Kawasaki 500 and 750 triples.

© Steve Harrison 02/03/2004

Shades of classic Z1 and H1
Part 2

After riding the GPZ around for a while I decided that I needed to make a few changes. For a start I was not happy with the power characteristics. The bike had plenty of top end but was pretty gutless down low. It also did not sound right. It had this weird sort of "beat" in the exhaust note. I knew what the problem was. The Microns had a 4:2:1 arrangement. In order to clear the deep GPZ sump the headers for cylinders 1&2 were about six inches longer than 3&4. That exhaust was pretty but it was never going to work properly.

The other issue was the riding position. I thought conventional bars would make for a nice comfy ride. Not so, I felt like I was flapping about in the breeze which did not help stability one bit. I needed more weight over the front wheel. The flogged out rear suspension was not helping either. This was easily fixed with a nice new Wilbers / Technoflex shock.

I found myself a good set of larger 34mm Mikuni CV carbs from an earlier model GPZ. I gave these a birthday and installed them along with the original air box. The Microns were sold and I fitted a set of Jama / Laser reproduction 4:2 headers and alloy cans. The idea being that 4:2 systems are supposed to improve bottom end power.

The 91 GPZ front end came with a top triple clamp and a nice set of alloy clip-ons with risers. It was a shame to have to throw out the ZRX750 clamp and headlight brackets but it had to be done. The 91 GPZ had the ignition switch mounted on the top clamp surrounded by a huge ugly casting. All of this had to be hacked off and filled in. Fortunately, the clamp was designed in such a way that I could remove all this junk without any fear of weakening it. I also needed to add a couple of lugs so I could mount the clocks. I had not used a TIG welder since my tech days, so it was an interesting job. I was worried that the different filler material would stand out like dogs. I used a rod that was supposed to be for welding cast Aluminium. Surprisingly, it turned out well. After much grinding and polishing you have to look really hard to notice any colour difference.

I then had to make up a set of headlight brackets and a tail tidy. The rear guard was binned and I fitted a set of mini GSXR indicators. The last step was to fill the holes in the ducktail where the original blinkers had been mounted. Now I was ready for paint. I knew exactly what I wanted. That fantastic two tone candy green used on the Kawasaki H1 and H2 triples.

There was no way I could afford to get the bike painted professionaly. I had been mucking about with paint and special effect pigments lately so I decided to give it a go. The first step was to shoot everything flat black. The areas that I wanted to be in a lime green were then masked up and sprayed white. I had a sample of this really interesting effect pigment that I got from some chemical company. I cannot remember who they were or what is was called. It was a white crystalline powder that looked like a fine semi transparent flake. Let’s call it crystal pearl. If you sprayed it on a black base it would come up a greyish white colour. Take it out in the sun and it reflected a heap of light and glittered like crazy. Cool, I can make use of this.

All done, lets ride
So I mixed a little crystal pearl with clear coat and dusted the black and white painted body work. Not a lot, just enough to reflect some light. Then it was 4 light coats of candy lime green. You have to be careful with this stuff. Candy is transparent and it’s easy to end up with stripes. Fortunately a lot of the job was black so it did not matter that much. I just had to spray evenly over the white areas. I then used 1/8 black and white pin striping tape to cover the joint between the black and white base coats and applied a couple of replica Kawasaki tank transfers from a 750 triple. Then it was on to the final clear coats. The first few coats were very light with plenty of drying time between. You have to build up the clear slowly because the solvents can attack the glue on the tape and transfers causing them to lift and/or bubble. The final couple of coats were heavier to give a nice gloss finish. I then let the job cure for a couple of weeks before a final cut and polish to a smooth glassy finish.

Mission accomplished. The bike was now much more comfortable at cruise and speed. The new riding position and rear suspension made for a big improvement in stability. You could now chuck it about with confidence. Bottom end power was much better and it still had plenty up top. As for the paint, you could not miss that Kawasaki green. In the shade, it was a very dark green bordering on black with lime green panels. Take it out in the sun and it lit up like a neon sign. I can see why professional paint jobs are expensive. You need a lot time and patience.

© Steve Harrison 06/04/2020